Spectrum selective radiation infrared stealth material and preparation method thereof
Technical Field
The invention belongs to the field of new materials, and particularly relates to a spectrally selective radiation infrared stealth material and a preparation method thereof.
Background
With the rapid development of the photoelectric technology, various reconnaissance technical means are generated. Stealth technology is increasingly well established in modern war. Among various stealth technologies, infrared stealth occupies a very important position. The infrared stealth refers to eliminating or reducing the difference of radiation characteristics of two atmospheric windows (3.0-5.0 μm, 8.0-14.0 μm) of middle and far infrared wave bands between a target and a background.
Currently, the use of low emissivity infrared stealth materials remains the dominant mode of infrared stealth. The traditional infrared low-emissivity material has low emissivity in the whole infrared band, and covers the bands of 3.0-5.0 μm and 8.0-14.0 μm of infrared detection. According to the Stefan-Boltzmann law: m ═ epsilon σ T4The degree of infrared radiation exitance is related to the temperature T and the emissivity epsilon. The traditional low-emissivity material mainly reduces the emissivity to reduce the degree of emergence of infrared radiation, so that infrared stealth is realized. However, according to the Stefan-Boltzmann law, the infrared radiation characteristic of the target is closely related to the temperature. An increase in temperature likewise leads to an increase in the degree of emergence of the radiation. For the traditional low-emissivity material, the low emissivity of the infrared full-wave band can reduce the efficiency of radiating heat by radiation of the target, so that the temperature of the target is rapidly increased, the infrared radiation characteristic of the target is enhanced, and the exposure possibility is caused. Therefore, selective radiation materials with low emissivity and radiation cooling performance are the development trend of infrared stealth materials. Specifically, the method comprises the following steps: in the infrared windows with wave bands of 3.0-5.0 μm and 8.0-14.0 μm, the material has low emissivity to avoid detection; in the non-window band, the material has high emissivity for radiative cooling. And starting from the two aspects of reducing the emissivity and reducing the temperature, the infrared radiation characteristic of the target is reduced, so that the infrared stealth is realized. Development of infrared stealth materials with selective radiation characteristics realizes compatibility of low emissivity and radiation heat dissipation, and represents the development trend of infrared stealth technology.
In recent years, researchers have become more and more sophisticated in the modulation of spectral radiation and have made progress in the fields of solar selective absorption coatings, civil radiation refrigeration technology, and the like. However, the use of selective radiation materials in the field of infrared stealth is still immature. Chinese patent CN104865617A discloses an infrared stealth film with spectral selectivity and low emissivity and a preparation method thereof, the infrared stealth film is formed by compounding germanium which is a high refractive index material and magnesium fluoride which is a low refractive index material, but the material structure and process are complex, the number of film layers is large, the film is thick, the internal stress of the material is increased, and the material structure is easily damaged in a high-temperature environment. Therefore, the research and development of the infrared stealth material with simple structure and spectrum selective radiation characteristics is of great significance.
Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects and shortcomings mentioned in the background technology and provide a spectrum selective radiation infrared stealth material with a simple structure and a preparation method thereof.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
the infrared stealth material for the spectrum selective radiation is of a layered structure and sequentially comprises a substrate, an aluminum nitride layer and a dielectric layer; the medium layer consists of a plurality of medium layers A and medium layers B which are alternately arranged; the dielectric layer A is made of any one of germanium, tellurium and silicon, and the dielectric layer B is made of any one of zinc sulfide, zinc selenide, magnesium fluoride, barium fluoride and calcium fluoride.
Preferably, the number of the infrared stealth materials is 4-7.
Preferably, the thickness of the aluminum nitride layer is greater than 0.5mm, and the thickness of the dielectric layer A and the thickness of the dielectric layer B are both 100-1000 nm. The change of the thickness of the film layer or the change of the layer number in the invention can cause the spectral characteristics of the material obtained in the invention to deviate from the preset target of the invention, and the thickness of each layer is controlled within the range, so that the spectral selective radiation material with better effect can be obtained.
In the infrared stealth material, preferably, the substrate is made of any one of silicon, glass, metal (such as aluminum, stainless steel, copper, nickel-based alloy), and polymer material (such as PE and PET).
Preferably, the aluminum nitride layer is in contact with the dielectric layer a.
Preferably, the reflectivity of the aluminum nitride layer in a wave band of 11-14 microns is more than 80%, and the emissivity in a wave band of 5-8 microns is more than 80%; the transmissivity of the dielectric layer A and the dielectric layer B at a wave band of 3-14 mu m is more than 50%, and the emissivity at the wave band of 3-14 mu m is lower than 5%.
As a general inventive concept, the present invention also provides a preparation method of the above infrared stealth material, comprising the steps of:
(1) cleaning and drying the substrate;
(2) preparing an aluminum nitride layer on the surface of the substrate by adopting a magnetron sputtering or tape casting method;
(3) and depositing a dielectric layer A and a dielectric layer B on the aluminum nitride layer by adopting magnetron sputtering or electron beam evaporation, and repeatedly and alternately depositing the dielectric layers A and the dielectric layers B until the designed number of layers is reached to finish the preparation of the infrared stealth material.
In the above preparation method, preferably, the cleaning is performed by cleaning with deionized water and then soaking in absolute ethyl alcohol for ultrasonic cleaning.
The emissivity, transmittance and reflectance of the material have the following relations: emissivity + transmittance + reflectance is 1. The aluminum nitride does not belong to an infrared transparent dielectric material, the emission and reflection characteristics of the aluminum nitride are utilized, a selective emission infrared stealth material is designed by combining a physical optical principle, specifically, the selective emission characteristic of the material is realized by utilizing the high reflection characteristic of an aluminum nitride layer in a 11.0-14.0 mu m waveband, the high emission characteristic in a 5.0-8.0 mu m waveband and the geometric optical principle of a multilayer dielectric film, and the top multilayer dielectric film has the following spectral characteristics through structural design: 5.0-8.0 μm has high transmittance, and 3.0-5.0 μm and 8.0-11.0 μm have high reflectance; the multilayer dielectric film is arranged on the upper part of the aluminum nitride layer, so that the low emissivity of window wave bands (3.0-5.0 μm and 8.0-14.0 μm) and the high emissivity of non-window wave bands (5.0-8.0 μm) required by infrared stealth can be met.
Compared with the prior art, the invention has the advantages that:
(1) the emissivity of the infrared stealth material with spectral selectivity radiation is below 0.30 at the infrared window wave band of 3.0-5.0 mu m and 8.0-14.0 mu m, and can reach more than 0.75 at the non-window wave band of 5.0-8.0 mu m.
(2) The spectrum selective radiation infrared stealth material has a simple structure and is convenient for large-area preparation and application.
(3) The invention selects the high-temperature-resistant aluminum nitride, simultaneously reduces the layer number and the total thickness of the dielectric film as much as possible, and can avoid the damage of the material structure caused by the stress problem at high temperature.
(4) The preparation process of the spectrum selective radiation infrared stealth material is simple and feasible, good in repeatability and low in equipment requirement.
Drawings
Fig. 1 is a schematic structural diagram of a spectrally selective radiant infrared stealth material in embodiment 1 of the present invention.
FIG. 2 is an emissivity spectrum of the spectrally selective radiation infrared stealth material prepared in example 1 of the present invention at a wavelength band of 3.0 μm to 14.0 μm.
Fig. 3 is an emissivity curve of the spectrally selective radiant infrared stealth material prepared in example 1 of the present invention at room temperature to 400 ℃.
Illustration of the drawings:
1. a substrate; 2. an aluminum nitride layer; 3. a first germanium layer; 4. a magnesium fluoride layer; 5. a second germanium layer.
Detailed Description
In order to facilitate an understanding of the invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of the invention is not limited to the specific embodiments below.
Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
Example 1:
the structure of the spectral selective radiation infrared stealth material is shown in figure 1 and sequentially comprises a silicon wafer substrate 1, an aluminum nitride layer 2 (with the thickness of 1mm), a first germanium layer 3 (with the thickness of 313nm), a magnesium fluoride layer 4 (with the thickness of 117nm) and a second germanium layer 5 (with the thickness of 313 nm).
The preparation method of the spectrally selective radiation infrared stealth material in the embodiment comprises the following steps:
(1) cleaning a silicon wafer by using deionized water, soaking the silicon wafer in absolute ethyl alcohol for ultrasonic cleaning, and drying;
(2) high-purity aluminum nitride powder is used as a raw material, and yttrium oxide (Y) is used as a sintering aid2O3) And Al2Y4O9Preparing the raw materials, a sintering aid, a conventional binder and a solvent to obtain casting slurry; obtaining a casting belt with uniform thickness by using a scraper casting method, and preparing an aluminum nitride layer with the thickness of 1mm on the surface of a silicon wafer through punching, laminating, degumming and sintering;
(3) and (3) depositing a layer of germanium with the thickness of 313nm (the deposition rate is 0.2nm/s) on the aluminum nitride layer by adopting an electron beam evaporation technology, then depositing a layer of magnesium fluoride with the thickness of 117nm (the deposition rate is 0.1nm/s), and then depositing a layer of germanium with the thickness of 313nm (the deposition rate is 0.2nm/s), thereby completing the preparation of the infrared stealth material.
The infrared emissivity of the spectrally selective radiant infrared stealth material prepared in this example is measured to be 3.0 μm to 14.0 μm, and as shown in fig. 2, the emissivity of the spectrally selective radiant infrared stealth material finally prepared in this example is 0.28 and 0.25 in the infrared window bands of 3.0 μm to 5.0 μm and 8.0 μm to 14.0 μm, respectively, and is about 0.78 in the non-window band of 5.0 μm to 8.0 μm.
The emissivity curve of the spectrally selective radiation infrared stealth material prepared in this example at room temperature to 400 ℃ was tested, and as shown in fig. 3, the curves at different temperatures substantially coincided with the emissivity curve at room temperature.
Example 2:
the invention relates to a spectrum selective radiation infrared stealth material, which sequentially comprises an aluminum sheet substrate, an aluminum nitride layer (with the thickness of 1.5mm), a first silicon layer (with the thickness of 345nm), a zinc sulfide layer (with the thickness of 227nm) and a second silicon layer (with the thickness of 342 nm).
The preparation method of the spectrally selective radiation infrared stealth material in the embodiment comprises the following steps:
(1) cleaning an aluminum sheet by using deionized water, soaking the aluminum sheet in absolute ethyl alcohol for ultrasonic cleaning, and drying;
(2) preparing an aluminum nitride layer with the thickness of 1.5mm on the surface of the aluminum sheet by adopting a magnetron sputtering method (direct current reactive sputtering, the power of 200W, the deposition temperature and room temperature, the flow ratio of nitrogen to argon of 1:2, and the deposition pressure of 0.8 Pa);
(3) and (2) depositing a silicon film with the thickness of 345nm (radio frequency sputtering, power of 150W, deposition temperature room temperature and deposition pressure of 0.5Pa) on the aluminum nitride layer by adopting a magnetron sputtering technology, then depositing a ZnS film with the thickness of 227nm (radio frequency sputtering, power of 100W, deposition temperature room temperature and deposition pressure of 0.3Pa), and then depositing a silicon film with the thickness of 342nm (radio frequency sputtering, power of 150W, deposition temperature room temperature and deposition pressure of 0.5Pa), thereby completing the preparation of the infrared stealth material.
The spectral selective radiant infrared stealth material prepared in the embodiment is tested to have the infrared emissivity of 3.0-14.0 μm, the emissivity of 0.28 and 0.26 respectively at the infrared window wave band of 3.0-5.0 μm and 8.0-14.0 μm, and the emissivity of 0.76 on the average at the non-window wave band of 5.0-8.0 μm.